Multiple-chamber rotary kiln



Filed Aug. 26, 1965 QQ/ E wok .6 ,m5 mm @im WA M w n m w United States Patent O 3,360,250 MULTIPLE-CHAMBER RGTARY KILN Magnus Malmberg, Mosbach, Baden, Germany, asslgnor to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen am Rhine, Germany Filed Aug. 26, 1965, Ser. No. 482,731 3 Claims. (Cl. 263-32) ABSTRACT OF THE DISCLOSUREl A rotary kiln for burning solid materials madevup of several overlapping pipe sections of different diameter,

the en-ds of the sections forming annular gaps through- This invention relates to apparatus for burning solid materials. More particularly, the invention relates to a multi-chamber kiln for burning waste products.

It is known that grate-fired furnaces may be used for the destruction of wastes. Grate firing is, however, unsuitable for materials that are liquefied vby heating, especially aggressive materials, because the liquefied materials iiow through the grate and may clog the .air inlets in the furnace wall with the result that the grate may be rendered unserviceable after a relatively short period of operation. It is therefore customary to use rotary kilns for burning liquid wastes; these kilns may be arranged after stationary grates over which the materials to be reacted are passed While still solid.

The intensity of the thermal reactions occurring in combustion processes depends ou an adequate supply of air or oxygen in each zone of the furnace. It is therefore of particular importance for the design of the furnace and the utilization of its capacity that the air necessary for combustion should be properly metered and that the air supplied to each combustion zone during each phase of the reaction of the materials to be burnt should be given the greatest possible turbulence. Generally speaking, the aim in the case of combustion furnaces using an excess of air, as opposed to gasification furnaces, is to thoroughly mix the air with the combustible gases and to make the mixture available uniformly over the whole combustion space. This requirement cannot, however, be fully satisfied in all cases. The rotary kilns of conventional design have the disadvantage that the air required over the whole length of the kiln has to be supplied at the feeder end of the kiln. Although the air is given a marked twisting movement while it is being supplied and other steps are taken to promote turbulence, it has been impossible to prevent zones of laminar flow occurring over the comparatively great length of the kiln. As a result of these turbulencefree zones combustion is incomplete, at least locally, and even if a considerable excess of air is supplied at the feeder end, there is a shortage of air at a plurality of points in the kiln. Besides, the supply of large amounts of air delays ignition of the fuel to be burnt when the kiln is started up, especially when the air has not been adequately preheated.

It is an object of the present invention to provide a rotary kiln in which the air is distributed over the Whole length of the combustion space in such a way that a local shortage of air is substantially avoided.

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This object is achieved by a rotary kiln according to this invention which is Idivided up a plurality of times along its length, thus forming sections to which the air is supplied separately. It is a special feature of the kiln according to the invention that the tube consists of a plurality of sections which are arranged in series and are of different cross-section and whose ends fit over one another, forming annular gaps that enable the air to be supplied separately to each section. Another feature is that a stationary jacket is provided, preferably around the sections of relatively small diameter, through the compartments of which the amount of air required for the combustion chamber of each section is supplied separately. A further feature of the invention is that the annular gaps existing between the sections are defined by surfaces of cone-shaped bodies, at least on the side of the combustion chamber. The surfaces defining the annular gaps preferably form different angles with the axis of the kiln around the circumference thereof, so that an intensive twisting movement is achieved and turbulence in the combustion chamber is improved without any additional steps.

The invention will now be described by way of example with reference to the accompanying drawing, in which FIGURE 1 shows a suitable embodiment of a rotary kiln according to the invention and FIGURE 2 shows a detail of such kiln.

Referring to FIGURE-1, rotary kiln 1 comprises three pipe sections A, B and C lined with refractories and having different cross-sections. The pipe sections increase in diameter in the direction of conveyance of the material to be burnt. Section A having the smallest diameter is charged with the material to be reacted, for example burnt, via a feed inlet 2, for example a chute or the like. T-he air required for the first zone of the kiln, defined by section A, is blown in alongside the material which is conveyed obliquely to axially. A system of bafiies 3 arranged at the inlet side of section A serves to produce a twisting movement which helps to accomplish the mixing of the air and the combustible gases formed in the first section. Section B is larger in diameter than section A so that it fits over the end of section A, leaving an annular gap 5. Similarly, the left end of section C fits over section B leaving an annular gap 5. The sections B and C which are larger in diameter than section A are preferably also longer than section A. By varying the diameter and length of sections A, B and C within certain limits, the gas velocity and the residence time of the material to be treated in the multi-chamber rotary kiln can be adapted to requirements.

The annular gaps 5 and 5 for the supply of air are angled with respect to the axis of the kiln on the side of the combustion space so that the air current entering the combustion space forms an acute angle with the axis of the kiln. To form the annular gaps 5 and 5', partly or completely cone-shaped bricks 6 and 7 are provided at the ends of linings 4 inside sections A, B and C, i.e. the bricks dening the gaps. To achieve intensive mixing of the air and any additional gaseous fuel supplied through gaps 5 and 5 with the gas formed in the combustion chamber, the direction 0f the air current, which depends upon the shape of bricks 6, 6', 7 and 7', may be varied over the circumference of the annular gaps 5 and 5. FIGURE 2 shows an embodiment of a rotary kiln according to the present invention in which an angle a1 formed by the direction of the air current with the axis of the kiln on one half of the circumference of the annular gap is somewhat smaller than angle a2 on the other half of the circumference, the transition from one angle to the other being sudden. Another possibility to improve the mixing effect in the kiln is to provide for a gradual rather than a sudden change of the angle a over the circumference of the gap. The planes forming angles x1 and u2 are prefer- 3 'ably arranged alternately at 180 in each subsequent section of the kiln or, where the angle changes gradually, provision may be made for the twisting movement to occur in the opposite direction in each subsequent section. Soiling or clogging of gaps 5 and 5 can be prevented to an adequate extent by arranging that the cone-shaped portions ofthe bricks 7 and 7' in the sections of smaller diameter extend over the cone-shaped ends of bricks 6 and 6 in the sections of larger diameter, as is shown in FIGURE 2.

To enable the air or other gaseous fuel being supplied through baffles 3 into section A and through annular gaps 5 and 5 into sections B and C, .a jacket pipe 8 is provided around sections A and B which also encloses the feed inlet of the kiln and whose diameter is similar to that of section C. The annular space between jacket pipe 8 and sections A and B is subdivided by partitions 9 and 9' substantially perpendlcularly to the axis, annular chambers 10a, 10b and 10c being formed. To provide a seal between stationary partitions 9 and 9 and rotating sections A and B, the inner edge of each partition runs in a groove which may consist for example of a pair of rings welded onto the sections and situated very close to one another. Obviously any other labyrinth type seal may be used as the seal required at these points. A similar seal is necessary between the right end of jacket pipe 8 and section C of the kiln.

Each annular chamber should have at least one pipe connection 11a, 11b or 11C. The pipes attached to these connections incorporate control instruments with which the lamounts of air or other gaseous or vaporous fuel to be supplied to sections A, B and C can be ajusted separately. The heat radiated to the outside from sections A and B is substantially absorbed by the gaseous or vaporous fuel passed through annular chambers 10a, 10b and 10c and thus carried off, those portions of the walls of the multi-charnber rotary kiln enclosed by annular chambers 10a, 10b and 10c being cooled Without any additional arrangements. The gases formed in the kiln during operation can be prevented from escaping through gaps 5 and 5' to an adequate extent by maintaining a slightly superatmospheric pressure of the gaseous or vaporous fuel in annular chambers 10a, 10b and 10c.

The individual sections A, B and C of the rotary kiln may be rigidly connected to each other to simplify the driving mechanism. It is, however, also possible to support them independently and to drive them either individually or in groups. For this purpose, the outer walls of the sections are provided with raiding rings in known manner. If independent drives are used, sections A, B, and C may, either individually or in groups, be driven at ydifferent angular velocities or if desired in opposite directions. Apart from the transport of the material to be treated throughout the length of the kiln, the sections then function independently.

Rotary kilns according to the present present invention are intended especially for burning waste products in waste disposal plants. They are, however, also suitable as reactors for reacting solid or partly liquid materials with gaseous or vaporous substances.

I claim:

1. A multi-chamber rotary kiln for the chemical reaction of solid materials which comprises: a. plurality of overlapping pipe sections of different diameter arranged in series, annular gaps between the ends of said sections, a rigid jacket arranged around the sections of relatively small diameter, movable seals between said jacket and said sections, and means for separately supplying air to each of said sections, the ends of said sections being coneshaped at least on the side of the combustion chamber, the surfaces of said cone-shaped ends dening said annular gaps and forming acute angles with the axis of said kiln.

2. A multi-chamber rotary kiln as claimed in claim 1 wherein said surfaces form an angle with the axis of said kiln which gradually changes over the circumference thereof.

3. A multi-chamber rotary kiln as claimed in claim 1 wherein said surfaces form an acute angle with the axis of said kiln over approximately half of the circumference thereof and form a different acute angle over the rest of the circumference thereof.

References Cited UNITED STATES PATENTS 1,250,554 12/1917 Bryan 110-14 1,583,436 5/1926 Atkinson 110-14 1,728,958 9/1929 Duncan 110--14 2,23 8,161 4/1941 Drew et al 110-14 FREDERICK L. MATTESON I R., Primary Examiner.

JOHN I. CAMBY, Examiner. 

1. A MULTI-CHAMBER ROTARY KILN FOR THE CHEMICAL REACTION OF SOLID MATERIALS WHICH COMPRISES: A PLURALITY OF OVERLAPPING PIPE SECTIONS OF DIFFERENT DIAMETER ARRANGED IN SERIES, ANNULAR GAPS BETWEEN THE ENDS OF SAID SECTIONS, A RIGID JACKET ARRANGED AROUND THE SECTIONS RELATIVELY SMALL DIAMETER, MOVABLE SEALS BETWEEN SAID JACKET AND SAID SECTIONS, AND MEANS FOR SEPARATELY SUPPLYING AIR TO EACH OF SAID SECTIONS, THE ENDS OF SAID SECTIONS BEING CONESHAPED AT ALEAST ONE THE SIDE OF THE COMBUSTION CHAMBER, THE SURACES OF SAID CONE-SHAPED ENDS DEFINING SAID ANNULAR GAPS AND FORMING ACUTE ANGLES WITH THE AXIS OF SAID KILN. 